1. Field of the Invention
The present invention relates to a purification process for an organic electronics material, an electroluminescent device middle layer material purified by the process, and an electroluminescent device employing the middle layer material.
2. Description of the Related Art
Electroluminescent devices have been attracting attention as, for example, large-area solid state light sources to replace incandescent lamps and gas-filled lamps. They have also been attracting attention as self-luminous displays, and are the most promising alternative to liquid crystal displays in the flat panel display (FPD) field. In particular, an organic electroluminescent (EL) device, in which the device material is formed from an organic material, is being commercialized as a low power consumption full-color FPD. Above all, polymer-based organic EL devices will be indispensable for future large-screen organic EL displays since the organic material of the polymer-based organic EL devices is formed from a polymer material for which film formation by printing, ink-jet, etc. is simple compared with low molecular weight-based organic EL devices, which require film formation in a vacuum system.
Conventionally, polymer-based organic EL devices employ either a conjugated polymer such as poly(p-phenylene-vinylene) (see e.g. International Publication WO90/13148) or a non-conjugated polymer (see e.g. I. Sokolik, et al., J. Appl. Phys. 1993. 74, 3584) as the polymer material. However, their luminescence lifetime as a device is short, which gives rise to problems when constructing a full-color display.
With the object of solving these problems, polymer-based organic EL devices having a middle layer between a light-emitting layer and an electrode have been proposed in recent years, but they are not satisfactory in terms of stability. This is due to impurities contained in a middle layer material and, in particular, the presence of Pd.